The field of the invention generally pertains to ignition devices for use with internal combustion engines. The invention relates more particularly to a glow plug construction utilizing an annular washer having a curvilinear upper surface, wherein the annular washer is secured inside the glow plug by crimping an upper rim of the glow plug body to contact and press upon a substantial portion of the curvilinear upper surface of the annular washer.
It is known for diesel and other spark-less internal combustion engines, such as those used for miniature radio-controlled models, to utilize a preheating device whereby the temperature is raised sufficiently to ignite a pressurized combustion chamber and initiate the engine cycle. Due to the high temperatures and pressures necessary for proper operation of these types of engines, it is critical that such preheating devices, commonly known as xe2x80x9cglow plugsxe2x80x9d, are adequately sealed to prevent pressure leakage therethrough. Oftentimes, however, leakage may occur through the electrically insulating seals separating two electrodes which provide electricity to a heating element of the glow plug. This can cause the engine to run lean and consequently damage the engine.
One known method for internally sealing glow plugs has been to crimp, i.e. plastically bend, an upper rim of an outer shell of the glow plug in a radially inward manner to exert pressure on the insular seals. Metallic washers are typically utilized as an intermediate element between the crimp and the insular seals to provide additional contact pressure which arises from thermal expansion of the metal. Additionally, for many glow plug configurations having a coaxial electrode arrangement, crimping operates to firmly secure a core electrode within an outer shell electrode.
For example, in U.S. Pat. No. 4,418,661, a glow plug is shown having a metallic pressure ring 40 placed on an incline or chamfered edge 39 of an insulating bushing 36. The upper end of the outer socket 11 is then rolled or bent over as seen at 41 to press-secure the metallic pressure ring 40 against the insulating bushing 36.
Additionally, in U.S. Pat. No. 4,437,440, a preheating device is shown having an upper end with a top end portion 12 contouredly bent around a metal packing 14 in contact with an electric insulated annular plug 13. As can be best seen in FIG. 1B, the metal packing 14 has a rounded outer edge, and the top end portion 12 is bent at most ninety degrees from vertical around the metal packing 14.
And similar to the ""440 patent, a glow plug is shown in FIG. 1 of U.S. Pat. No. 5,834,736 having a top end portion countouredly bent to secure an electrical insulator 31 having a rounded outer edge. The crimped portion of the top end portion is also at most ninety degrees from vertical around the electrical insulator 31.
While crimping alone, or in conjunction with a metallic washer, operates to provide some pressure for internally sealing glow plugs, the ultimate configuration of the crimp as well as the manner in which the crimp is formed, often determines how well the glow plug is actually sealed. In this regard, the crimping portions 47 shown in the ""661 patent may experience high localized stresses when crimped at such a sharp angle shown in FIG. 1. This may reduce the life cycle of the glow plug by failing along the crimp angle.
Furthermore, the necessary impact force required to produce and thereafter consistently maintain the crimp at such sharp angles has been known to distort and warp the plug body. Such impact forces are typically adjusted to a greater magnitude to compensate for a limited resilient-rebounding effect of the crimping portions subsequent to crimping. Thus, it would be advantageous in a glow plug crimping process to crimp glow plugs without exerting an impact force thereon.
Additionally, while both the ""440 and ""736 patents disclose crimp portions contoured to respective curvilinear surfaces, they are angled at most ninety degrees from vertical. The degree of surface contact resulting from this arrangement, however, may be inadequate to supply the necessary crimping pressure to effectively internally seal the glow plug.
It is an object of the present invention to provide a glow plug construction internally pressure sealed to prevent pressure leakage therethrough.
It is a further object of the present invention to provide a glow plug construction which utilizes a metallic washer having a curvilinear upper surface against which a crimp portion of the glow plug substantially contacts for exerting substantial contact pressure thereon.
It is a still further object of the present invention to provide a glow plug construction wherein, upon crimping a crimp portion of the glow plug around a metallic washer having a curvilinear upper surface, an end portion of the crimp portion extends past and below an apex of the upper surface.
It is a still further object of the present invention to provide a crimping method for internally pressure sealing a glow plug construction to prevent pressure leakage therethrough.
It is a still further object of the present invention to provide a crimping method for crimping a crimp portion of a glow plug construction to substantially contact a metallic washer having a curvilinear upper surface for exerting substantial contact pressure thereon.
It is a still further object of the present invention to provide a crimping method wherein upon crimping a crimp portion of the glow plug around a metallic washer having a curvilinear upper surface, an end portion of the crimp portion extends past and below an apex of the upper surface.
The present invention is for a glow plug construction for use in internal combustion engines. The glow plug construction comprises a first electrode which is an outer shell having a central bore, and an upper surface with a crimp portion extending to an upper rim terminus. The glow plug construction also comprises a second electrode which is an elongated rod-like core extending through the open upper end into the central bore of the outer shell. The rod-like core is spaced from and supported against the outer shell by at least an insulating upper support element which is positioned adjacent the open upper end of the outer shell. Heater means is electrically connected to the first and second electrodes for producing heat when electricity is passed therethrough. And the glow plug construction has an annular washer having opposing upper and lower washer surfaces surrounding a central aperture. The upper washer surface has a perimetric ridge portion with a convex radial cross-section. In a preferred embodiment, the upper washer surface also has an annular deck portion adjacent the central aperture and surrounded by the perimetric ridge portion. The annular washer is positioned in the central bore at the open upper end such that the lower washer surface abuts against the upper support element, and the rod-like core non-tactually extends through the central aperture of the annular washer. The crimp portion of the outer shell is crimped radially inward to abut against a substantial portion of the perimetric ridge portion of the annular washer, such that the upper rim terminus is extended past and below an apex of the perimetric ridge portion.
The present invention is also for a crimping method for producing the glow plug construction described above. The method comprises providing a partially-assembled glow plug construction with a yet unbent crimp portion, and providing a crimping die having an annular die cavity with a die surface radially extending between inner and outer die rims. The annular die cavity has a concave radial cross-section greater than and generally proportional to the convex radial cross-section of the perimetric ridge portion of the annular washer. The crimp portion of the outer shell is then aligned with the die surface of the annular die cavity at the outer die rim, such that the crimp portion may slidably contact the die surface at the outer die rim when entering the annular die cavity. Then the partially-assembled glow plug and the crimping die are moved relative to and towards each other along a longitudinal axis of the glow plug, such that the crimp portion of the outer shell is bent radially inward by the die surface to abut the crimp portion against the perimetric ridge portion of the annular washer. And finally, the relative movement is stopped when the upper rim terminus extends at least past and below an apex of the upper washer surface.